Cataracts

What is a cataract?

When light enters the eye through the pupil, the image of the outside world is focused onto the back of the eye (the retina) so that a clear picture is sent to the brain. Most of the focusing is done by the front of the eye (the cornea) but the 'fine tuning' is done by a lens in the middle of the eyeball. The lens is made of a thick capsule filled with a clear substance. Sometimes this substance becomes cloudy and this is then called a cataract.

How do they occur?

The commonest cause of cataracts is old age, although in rare cases a baby can be born with them. Most people will eventually develop some signs of cataracts if they live into old age. However, there are some instances in which cataracts form earlier. For instance, diabetics are more prone to cataract formation, as are people on certain drugs such as steroids. Traumatic eye injuries sometimes cause cataracts to form and it is thought that some forms of radiation may lead to cataracts.

What are the symptoms?

In the early stages a cataract may not cause any symptoms and is frequently only noted when the person goes for a routine eye test when it is seen by the optician. As the cataract gets worse it causes vision to be impaired in the affected eye(s) causing a mistiness or sometimes the impression of dark blobs in the eye. These visual problems cannot be corrected by spectacles and therefore an optician will advise the person to go to their doctor. Cataracts do not themselves cause eye pain or redness so if these symptoms occur, especially if they are associated with worsening vision, medical advice should be sought immediately.

If the cataract is not treated it may get worse to the point where the eye becomes blind. In rare instances a very bad cataract may cause the eye to become inflamed with a resulting increase in pressure inside the eyeball, which may damage the main nerve carrying signals to the brain thus leading to irreversible blindness.

How is a cataract diagnosed?

Cataracts are fairly easy to diagnose. Even if the individual does not complain of any symptoms, blobs near the front of the eye or a general mistiness of the lens can be seen by an optician or doctor when they examine the eye with a special torch called an ophthalmoscope.

What is the treatment?

The only way to treat a cataract is to surgically remove it. A physician will help to advise on the best time to be referred to a specialist for the operation since surgery is only necessary if the cataract is causing visual difficulty. The specialist initially performs a careful examination of the eye to make sure that there are no other causes for the visual problems. For instance there would be no point performing a cataract extraction on a person suffering from another irreversible eye problem such as ageing of the back of the eye (macular degeneration). Also severe glaucoma can sometimes reduce the chances of a successful return of vision following cataract removal.

Occasionally the surgeon will perform an ultrasound examination of the eye if the cataract itself prevents him from properly assessing the eye with the usual instruments.

Techniques used in cataract surgery have improved over recent years. Years ago the procedure involved removing the cataract through an incision in the eye and then providing the patient with thick spectacles to make up for the loss of the lens. Nowadays the cataract is replaced with a tiny lens which is actually placed inside the eye. The operation is usually performed under local anaesthetic which sometimes involves injections around the eye or sometimes just local anaesthetic drops into the eye. It may be done as a day-case operation or during an overnight stay in hospital.

Various techniques are used to remove the old lens and replace it with a new one. Until recently the main method used was to make a 5mm cut at the edge of the iris (the coloured part of the eye), remove the cataract through an incision in the capsule (envelope) of the lens and then place a plastic lens on the back of the old lens capsule which is left behind. The cut was then stitched with very fine sutures which were often not dissolvable. This technique is still used in about 25% of cases.

A newer technique called phaco-emulsification is now used in most cases. This involves a special ultrasound probe being inserted into the lens to liquify the cataract which is then 'sucked' out. A smaller folding lens is then implanted. The advantage of this method is that a smaller 3mm hole is needed at the edge of the iris which often does not need any stitches. This technique is not suitable in every case.

Are there after effects?

Immediately after the operation the eye may be slightly sore and the vision a little cloudy but both of these symptoms usually subside rapidly although the eye may remain red for a few days. Most people are allowed home soon after the operation but the surgeon usually arranges to see the patient again within a few days to check that all is well. A variety of eye drops are usually prescribed for up to a month after the operation. These reduce the inflammation and maintain a normal eyeball pressure. Sometimes the specialist will advise an eye patch to protect the eye for a while and frequently patients are given advice about avoiding certain activities in the days after the operation such as heavy lifting, straining, bending and coughing. These activities may dislodge the new lens in the immediate post -operative period.

What is the outcome?

Generally speaking cataract surgery is very successful, resulting in a huge improvement in vision in almost all cases. However, as with any operation there are occasional complications. Sometimes the eye can become sore, blurred and sticky indicating an infection requiring urgent treatment and in certain cases the tiny stitches may need to be removed either because they become uncomfortable or they may cause distortion of vision making prescribing of suitable glasses difficult. In rare cases an infection inside the eye may cause permanent blindness in that eye. A late complication can occur when the lens capsule (which is left inside the eye) itself becomes cloudy and thick causing the eyesight once again to slowly deteriorate. However this can be treated with a special laser known as YAG laser which cuts a hole in the capsule allowing light to enter freely again, thus restoring clear sight.